What happens if you only eat one meal for a month?

The one-meal-a-day (OMAD) diet, an extreme form of intermittent fasting, has seen a surge in popularity, but a 2023 study found that skipping main meals is associated with increased mortality risk. For a month, this eating pattern forces significant metabolic and physiological changes, both positive and negative.

Quick Summary

Following the OMAD diet for a month can lead to weight loss, metabolic flexibility, and cellular repair, but it also increases the risk of nutrient deficiencies, fatigue, muscle loss, and hormonal disruptions.

Key Points

• Weight loss is likely but not guaranteed: Due to severe calorie restriction, most people will lose weight and fat, but results are not guaranteed and can be accompanied by muscle loss.

• Nutrient deficiencies are a major risk: It is extremely challenging to get all necessary vitamins, minerals, protein, and fiber from a single meal, which can lead to long-term health issues.

• Metabolic changes occur: The body shifts to burning stored fat for fuel, which can improve insulin sensitivity and trigger cellular repair (autophagy).

• Energy and mood fluctuations are common: Initial periods may cause fatigue, headaches, and irritability as the body adapts to low blood sugar, although some report increased focus later.

• Not a long-term solution: Health experts caution against prolonged OMAD due to sustainability challenges and potential risks, suggesting that more moderate eating patterns are safer.

• Medical consultation is crucial: Individuals with pre-existing conditions like diabetes, or pregnant and breastfeeding women, should avoid OMAD without strict medical supervision.

• Social life can be impacted: Eating patterns can disrupt social engagements and lead to feelings of isolation.

Understanding the OMAD Diet

The One Meal A Day (OMAD) diet is an aggressive form of time-restricted feeding, often referred to as the 23:1 method, where all daily calories are consumed within a single 1- to 2-hour window. For the remaining 22 to 23 hours, a person fasts, consuming only non-caloric beverages like water, black coffee, or unsweetened tea. Over a one-month period, this extreme restriction triggers significant metabolic adaptations in the body, which can be both beneficial and detrimental depending on an individual's health, diet composition, and physical activity level.

The Physiological Changes After One Month of OMAD

After a month on the OMAD diet, the body undergoes a metabolic shift. As carbohydrate stores (glycogen) are depleted during extended fasting, the body begins to burn fat for fuel, a process known as ketosis. This metabolic flexibility is one of the primary mechanisms driving weight loss and can lead to increased fat oxidation during exercise. Cellular renewal, or autophagy, is also enhanced during prolonged fasting periods, helping to clear out damaged cells and potentially offering anti-aging benefits.

**Potential Benefits:

• Significant Fat Loss: By consuming all daily calories in a single, short window, most people naturally create a calorie deficit, leading to weight and fat loss.
• Improved Insulin Sensitivity: Extended periods of low insulin levels can increase the body's sensitivity to insulin, which is beneficial for managing blood sugar levels and may reduce the risk of type 2 diabetes.
• Mental Clarity: Some people report improved mental clarity, focus, and energy levels during their fasting periods, potentially due to the body's use of ketones for brain fuel.
• Autophagy and Reduced Inflammation: The cellular repair processes triggered by fasting can help reduce chronic inflammation, a risk factor for many diseases.

**Significant Risks:

• Nutrient Deficiencies: It is extremely difficult to consume a sufficient quantity and variety of nutrients, including vitamins, minerals, protein, and fiber, in a single meal. Over time, this can lead to serious deficiencies and health problems.
• Muscle Mass Loss: While OMAD can lead to fat loss, it also poses a significant risk of muscle atrophy, especially if protein intake is insufficient or exercise is not included.
• Slowed Metabolism: Prolonged, severe calorie restriction can cause the body to adapt by slowing its metabolic rate to conserve energy, potentially leading to weight plateaus and future weight regain.
• Hormonal Imbalances: Long fasting periods can disrupt hormonal balance, particularly in women, potentially affecting menstrual cycles and increasing stress hormones like cortisol.
• Digestive Issues: Consuming a large meal in one sitting can cause digestive discomfort, bloating, and other issues. In some cases, it can trigger loose stools or constipation.
• Elevated Cholesterol: Some studies have indicated that eating one large meal a day may increase total and LDL ('bad') cholesterol levels and potentially raise blood pressure.

OMAD vs. Traditional Balanced Eating: A Comparison

Feature	One Meal A Day (OMAD)	Traditional Balanced Diet
Weight Management	Can cause rapid weight loss due to severe calorie restriction, but may be unsustainable and risk muscle loss.	Promotes gradual, sustainable weight loss with less risk of muscle loss when properly managed.
Nutrient Intake	High risk of nutrient deficiencies as it is challenging to get all necessary vitamins, minerals, and fiber in one meal.	Easier to meet daily nutrient needs by distributing intake across multiple meals.
Energy Levels	Initial fatigue and irritability are common during adaptation, but some report sustained energy after their body adapts to fat burning.	Generally provides stable energy throughout the day, preventing crashes and mood swings associated with low blood sugar.
Metabolic Health	Can improve insulin sensitivity and increase fat oxidation, but may also lead to metabolic slowdown and increased LDL cholesterol.	Offers consistent metabolic support without the extreme fluctuations, with well-documented benefits for cardiovascular health.
Sustainability	High dropout rates reported due to extreme hunger, fatigue, and social challenges. Not recommended long-term.	Easier to sustain as it fits into most social situations and does not cause severe restriction.
Risk of Disordered Eating	Restrictive nature can trigger or exacerbate disordered eating behaviors, including binge eating.	Less likely to promote unhealthy eating patterns due to its balanced and flexible approach.

Potential Complications and What to Watch For

For a month on OMAD, it is crucial to listen to your body and recognize signs of potential complications. A significant risk for people with underlying medical conditions, such as diabetes or low blood sugar, is hypoglycemia, which can cause shakiness, weakness, and confusion. The extreme restriction can also negatively impact mental health, causing irritability, fatigue, and food preoccupation.

In addition to the physical side effects, the social aspect of eating one meal a day can be challenging. Many social events revolve around shared meals, and OMAD can lead to feelings of isolation and make dining out complicated. The long-term effects of OMAD are not well-studied, with some research suggesting a higher risk of cardiovascular mortality associated with skipping meals.

Conclusion

Eating one meal a day for a month is an extreme form of intermittent fasting that can lead to rapid weight and fat loss, improved insulin sensitivity, and enhanced cellular processes like autophagy. However, these potential benefits are accompanied by significant risks, including nutrient deficiencies, muscle mass loss, metabolic slowdown, hormonal issues, and digestive problems. The diet is difficult to sustain long-term and may not be suitable for everyone, especially those with pre-existing medical conditions, a history of disordered eating, or women of reproductive age.

While some people report positive short-term results, the risks often outweigh the benefits for long-term health and sustainability. Before attempting an extreme diet like OMAD, consulting with a healthcare professional or registered dietitian is strongly recommended to determine the safest and most effective approach for your individual needs. For many, a more moderate and balanced eating pattern, or a less restrictive form of intermittent fasting, is a more sustainable path to achieving health and wellness goals.

Visit the National Institutes of Health for more research on fasting and health.

Frequently Asked Questions

Is it safe to eat only one meal a day for a month?

For most healthy adults, short-term OMAD may be safe, but a month is considered a prolonged period with a high risk of nutritional deficiencies, muscle loss, and other side effects. It is not recommended without medical guidance, especially for individuals with underlying health conditions.

How much weight can you lose on OMAD in a month?

Weight loss on OMAD varies, but research indicates an average of 4 to 8 pounds per month, though some see more. Initial losses may include water weight, and progress slows as metabolism adapts.

Can you build muscle on the OMAD diet?

Building significant muscle on OMAD is challenging because it's difficult to consume enough protein and calories in one meal to support muscle growth and recovery. Maintaining muscle mass is more likely than gaining it.

What are the most common side effects of OMAD?

Common side effects include hunger, fatigue, headaches, irritability, bad breath, and digestive issues like bloating or constipation. These symptoms often subside as the body adapts, but nutrient deficiencies can lead to more serious issues.

Does OMAD slow down your metabolism?

Yes, extreme calorie restriction for prolonged periods can cause your metabolism to slow down as the body enters 'starvation mode' to conserve energy. This can make future weight loss more difficult.

What should you eat for your one meal on the OMAD diet?

Your meal should be extremely nutrient-dense, including a balanced mix of lean protein, healthy fats, complex carbohydrates, and plenty of fruits and vegetables to combat nutrient deficiencies. A wide variety of whole foods is essential.

Who should not try the OMAD diet?

OMAD is not recommended for pregnant or breastfeeding women, children, older adults, individuals with diabetes, or those with a history of eating disorders. People with certain chronic conditions or those on medication should also avoid it unless directed by a doctor.